for(j in 1:max(clustering$cluster))
{
plot.default(x = NA, xlim = c(1, 12), 
             ylim = c(min(y), max(y)), xlab = "Time", ylab = "Expression changes", 
             main = paste("Cluster", j), axes = FALSE)

  axis(1, 1:12, c(1:12))
  axis(2)
}